FOREST PARK, Ill. (AP) — As many as four dozen people were injured when two Chicago commuter trains crashed in a western suburb during Monday morning rush hour, though none of the injuries appeared to be life threatening, officials said.

The crash happened when an empty Chicago Transit Authority train was traveling eastbound and hit a westbound train that was carrying passengers and stopped at the Blue Line’s Harlem station in Forest Park, CTA spokeswoman Lambrini Lukidis said. Forest Park is about 10 miles west of downtown Chicago.

“We were stopped at Harlem and then we hear like a big boom sound and everyone started flying out of their seats,” said passenger Lyneisha Fields. The 18-year-old said she was taken to a local hospital’s emergency room because she hit the back of her head on a metal bar in the train.

Lukidis said 33 people suffered non-life threatening injuries. Forest Park Mayor Anthony Calderone said he was told as many as four dozen people were injured, most reporting back and neck pain, and were taken to local hospitals.

“None were serious injuries thank god,” he said.

Lukidis said the eastbound train was traveling on the same track as the westbound train when the accident occurred along the Blue Line, which runs from O’Hare International Airport on the city’s northwest side to downtown Chicago, where it runs underground, and then west to Forest Park.

A section of one train car was crushed, resembling an accordion.

“We’re clearly investigating as to the cause of the incident,” Lukidis said, including why both trains were on the same track.

Firefighters from as many as a dozen local fire departments responded, Calderone said. Calls seeking comment from the Forest Park fire department weren’t immediately returned.